Jeff Lewis, left, a Juno spacecraft engineer and Kelly Bezak, the lead ace, watch a tracking screen at Lockheed Martin during the portion of the mission where the team lost the craft's signal. The Juno mission is midway through its journey to Jupiter and came close to Earth today as it was getting a gravity-assist "slingshot" around Earth.

Juno, shown in an artist's rendering, is scheduled to arrive at Jupiter in 2016.

Everything was going as planned when NASA’s Juno spacecraft entered a 22-minute communication black hole Wednesday afternoon, zooming within 347 miles of Earth’s surface on its slingshot trajectory toward Jupiter.

When the spacecraft reemerged from Earth’s dark side, the laughter quickly subsided at mission operations at Lockheed Martin Space Systems in Jefferson County.

Juno was emitting an unexpectedly weak signal, and scientists around the globe knew something was off.

“There’s always the chance that the spacecraft will do something unexpected,” said Tim Gasparrini, Lockheed’s Juno program manager.

About an hour later, the team had their answer: The spacecraft had put itself into safe mode at some point during the blackout period, but they didn’t know why.

“Safe mode is where it goes when it detects something it didn’t expect,” Gasparrini said. “We are still trying to sort out why that happened. … The team is going to spend tonight trying to figure it out.”

While the safe mode trigger is still unclear, the event itself is not catastrophic to the mission, which aims to help scientists understand Jupiter’s origins, atmosphere and whether it has a solid core.

The team was able to regain full communication with the spacecraft and could tell that it was on its proper trajectory.

“Safe mode is precisely that — safe,” said Marco Caceres, senior space analyst for the Teal Group. “It kind of turns off all major systems until they figure out what is wrong. Something is not quite right, but it is too early to speculate.”

Lockheed Martin designed, built and tested the spacecraft for NASA. It was launched in August 2011 on a United Launch Alliance Atlas V rocket. While that rocket is powerful, it doesn’t provide enough force to push the spacecraft, with its eight scientific instruments, all the way to Jupiter. So Lockheed devised two deep space maneuvers implemented a year into the mission that redirected Juno back toward Earth.

Wednesday’s flyby was not just for looks; it provided the needed gravity assist to essentially fling the spacecraft from 78,000 mph to 87, 000 mph.

In many ways, the event highlighted how fortuitous the Earth flyby was and how complicated these missions can be. Juno’s flyby was the first and only time it would enter a solar eclipse and be forced to rely on its battery for power, and it was the first and only time mission operations would be able test its instruments and sequenced commands on another planet before reaching Jupiter.

“If there’s any weaknesses that the safe mode identified, we have the entire cruise to Jupiter to figure it out,” Gasparrini said. The journey lasts about another two and a half years, arriving at the distant planet’s orbit July 4, 2016.

Meanwhile, NASA — the agency that commissioned the mission — was radio silent itself because of the partial government shutdown. When an event like Wednesday’s occurs, normally it would be tweeting and providing statements throughout the day. Instead, that burden fell on its prime contractor, Lockheed.

Caceres noted that the $1.1 billion Juno mission is a highly sophisticated spacecraft, so any number of major or minor anomalies may have occurred.

“In a lot of ways, you do want it to go into safe mode — if something goes wrong,” Caceres said. “I would certainly give them days, if not weeks because this is a long mission, and it’s pretty complex.”

Kristen Leigh Painter was a former business reporter who focused on airlines and aerospace coverage. She joined The Post in September 2011 and departed for the Minneapolis Star-Tribune in August 2014. She graduated from the University of Colorado Boulder with a master's in journalism after earning a bachelor's in history from the University of Wisconsin La Crosse.

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